Electrodeposited copper foil with carrier foil is being used in fields of electric industries or electronic industries as raw materials for manufacturing of printed wiring board and the like. Applying of the electrodeposited copper foil with carrier foil has begun as a result of requirements for thinning and fining pitch of the printed wiring boards and the like. It consists of a carrier foil and a thin copper foil (hereinafter also to be referred to as “bulk copper layer”), which is formed by electrolytic deposition on a surface of the carrier foil via a bonding interface layer and the like to have required thickness of around several μm, such as 3 μm or 5 μm, for example. The carrier foil, which is a foil usually having a thickness of around 18 μm to 35 μm, is used for reinforcing a thin bulk copper layer with low mechanical strength due to its thickness of around several μm. As carrier foil, for example, copper foil is mainly used. The copper foil for use as carrier foil has thicker and tougher mechanical strength than the copper foil employed as a bulk copper layer.
Here, on the surface side of the bulk copper layer in the electrodeposited copper foil with carrier foil which does not face the carrier foil, that is a surface side of direction for thickness increasing of the bulk copper layer by electrolytic deposition (hereinafter also to be referred to as “the deposition side surface of bulk copper layer”), various kinds of treatments are usually carried out: such as a roughening treatment, e.g., a nodular treatment and the like of the surface of the copper layer, an inorganic treatment, such as plating with a metal element, or an organic treatment of applying a silane coupling agent and the like in consideration of a bonding ability or a shelf life. In the present specification, a bulk copper layer that has been subjected to the above described roughening treatment will be also called a “bulk copper layer”, while the layer formed during an inorganic rust proofing treatment is also called an “inorganic treated layer”. In addition, in the present specification, the surface of the inorganic treated layer formed on the bulk copper layer is also called an “inorganic treated layer surface”.
In case of manufacturing a printed wiring board with the above described electrodeposited copper foil with carrier foil, the bulk copper layer portion is usually used as a circuit forming material, and therefore a printed wiring board is manufactured generally along steps as follows. That is, at first, an inorganic treated layer surface formed on the deposition side surface of the bulk copper layer or, as required, a silane coupling agent layer formed on the surface of a bulk copper layer are brought into contact with the pre-preg (FR-4 substrate and the like), and they are bonded together by hot pressing, and thus the resin substrate layer has been hardened to obtain a copper-clad laminate with a carrier foil. Here, for the purpose of simplifying the description, further details with regard to the inorganic treated layer and the silane coupling agent layer will be omitted.
Next, the carrier foil is released from the copper-clad laminate to obtain a copper-clad laminate consisting of the bulk copper layer and the resin substrate layer. Next, after the bulk copper layer surface of the copper-clad laminate is subjected to acid cleaning with diluted acid, and the bulk copper layer is etched with an etching solution such as copper chloride solution and the like to obtain a circuit. Here, in the above described step, by hot pressing one sheet of electrodeposited copper foil with carrier foil with a resin impregnated base material, derives a single-sided printed wiring board, while by employing two sheets of electrodeposited copper foil with carrier foil on both sides of a resin impregnated base materials, derives a double-sided printed wiring board.
A printed wiring board in recent years is often used as a multilayer printed wiring board with circuits in multiple layers. In this case, the following steps are usually carried out. That is, a plurality of double-sided printed wiring boards usually with respectively different circuit patterns are produced by the above described manner, and resin impregnated base materials are sandwiched between these double-sided printed wiring boards and undergo hot pressing to laminate to obtain a multilayer printed wiring board.
In the case of a double-sided printed wiring board or a multilayer printed wiring board, circuits that are sandwiched between one or more layers of resin substrate are electrically connected. To do so, “through holes” or “via holes” and the like as a penetrated hole or a blind hole are formed by laser drilling and the like. Then they are subjected to desmear processing with an alkaline potassium permanganate solution and the like to remove smears in the holes, followed by copper plating.
As a method of releasing carrier foil that is not useful in the step of manufacturing the above described single-sided printed wiring board or double-sided printed wiring board, a method of peeling along a bonding interface layer, that has been formed between the carrier foil and the bulk copper layer and which has a comparatively weak bonding strength, or a method of etching away the carrier foil is employed. A type of electrodeposited copper foil with carrier foil corresponding with the former method is called electrodeposited copper foil with carrier foil of a peelable type. While a type of electrodeposited copper foil with carrier foil corresponding with the latter method is called electrodeposited copper foil with carrier foil of an etchable type. Among them, since the latter has drawback in that it costs much for etching equipment and the like, in recent years, the peelable type of the electrodeposited copper foil with carrier foil has become in wide use.
Since the use of the above described electrodeposited copper foil with carrier foil enables to make the thickness of the bulk copper foil thin by securing the strength level by the carrier foil, thinning of printed wiring boards, enhancement in miniaturizing and light weight and fining of circuits and the like can be designated when compared with the case of using copper foil with conventional thickness. In particular, the electrodeposited copper foil with carrier foil of a peelable type has become preferable for use due to its easy releasing of the carrier foil and for its low cost.
However, in electrodeposited copper foil with carrier foil, a bulk copper layer is very thin with thickness of around 3 μm or 5 μm and the deposition side surface of bulk copper layer is smooth, and therefore bonding the deposition side surface of bulk copper layer, the surface of inorganic treated layer formed on the deposition side surface of bulk copper layer or a silane coupling agent layer formed as required and a resin substrate layer often shows too low bonding strength, and is hard to use in manufacturing a printed wiring board. Therefore, usually a roughening treatment by electrolyzing the electrodeposited copper foil with carrier foil in a copper electrolytic solution to form minute copper particles and the like on the deposition side surface of the bulk copper layer is carried out to increase the roughness, followed by a process of forming an inorganic treatment layer or a silane coupling agent layer. This allows to increase the bonding strength between the bulk copper layer and the resin substrate layer.
However, in recent years, decrease in roughness of a deposition side surface of bulk copper layer as much as possible is demanded in order to fulfill features such as a finer circuit, a migration resistance and a controlled impedance. However, when a roughening treatment is carried out leading to a decreased roughness, a problem arises that the bonding strength is hard to increase as required. Therefore, electrodeposited copper foil with carrier foil having high bonding strength has been required more and more, either without or with the roughening treatment described above providing lower roughness on the bulk copper layer.
In addition, the electrodeposited copper foil with carrier foil having a thickness of the bulk copper layer of 3 μm or more does not show a defect of pin holes and the like, since electrolytic deposition may fill pin holes and the like. But generally, in the case where the thickness of the bulk copper layer is less than 3 μm and very thin, and a roughening treatment is not carried out or is not carried out sufficiently, pin holes and the like are not filled successfully and the pin holes and the like may remain. Therefore, in any type of printed wiring board, such as single-sided printed wiring board, double-sided printed wiring board or multilayer printed wiring board, a problem arrives that an inorganic rust proofing layer usually present at the interface between the bulk copper layer and the resin substrate layer is corroded by an acid cleaning solution, an etching solution or a desmear solution inside the pin holes and the like at the time of production thereof, the interface may create delamination, and a circuit formed on the delaminated portion is easily peeled off. In particular, as described above, in electrodeposited copper foil with carrier foil of a type without a roughening treatment on the deposition side surface of the bulk copper layer or with a roughening treatment to provide low roughness, an interface between the bulk copper layer and the resin substrate layer is bonded with a surface in smooth or similar state, and therefore an acid cleaning solution, an etching solution or a desmear solution will easily spread over a wide area into the above described inorganic treated layer compared with a conventional type of electrodeposited copper foil with carrier foil that is carried out a roughening treatment to provide a comparatively high roughness onto the deposition side surface of bulk copper layer. Therefore, a problem that a circuit peels off easily will come out.
Moreover, in case of producing a double-sided printed wiring board or a multilayer printed wiring board with conventional electrodeposited copper foil with carrier foil, such a problem comes out that an inorganic treatment layer usually present on the interface between the bulk copper layer and the resin substrate layer exposed in the side wall of holes such as through holes or via holes and the like is corroded by a desmear solution at the time of a desmear process and may create delamination, and a circuit formed on the delaminated portion may peel off.
Due to the above described situations, an electrodeposited copper foil with carrier foil is required having a bonding strength high enough between the deposition side surface of a bulk copper layer or the surface of an inorganic treated layer and the resin substrate layer, even when roughness of the deposition side surface of the bulk copper layer or of the surface of the inorganic treated layer is low. Also, it is desired that the interface between the bulk copper layer and the resin substrate layer is hard to delaminate, even when contacted with an acid cleaning solution, an etching solution or a desmear solution where pin holes and the like remain in the bulk copper layer or the side wall in the holes of through holes or via holes and the like.
In contrast, a prior art related to electrodeposited copper foil with carrier foil of a peelable type, JP-A-2000-309898 (Patent Document 1), for example, discloses electrodeposited copper foil with carrier foil, comprising a bonding interface layer being formed on a surface of carrier foil with an organic agent, and with electrodeposited copper foil layer being deposited and formed on the bonding interface layer. It is discussed that by using such an electrodeposited copper foil with carrier foil, the stability is high in peeling during releasing the carrier foil and therefore a yield of production can be improved greatly.
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-309898 (first column on Page 2)